Ray and friends, I am always curious in the days of flip chip BGA's how does one view the pwr/gnd loop inductance of a package ? Does the core pwr/gnd current really flow through the BGA pwr/gnd planes or does it really flow straight up from the C4 bump under the die through the via from the PCB ? Does the presence of power/gnd planes in a BGA is more to do with referencing the I/O and for the switching current to return. In the later case measuring the pwr/gnd loop inductance is meaningless unless the on die decoupling is presence and a specific I/O loop is known. In other words, why do we even need to measure the pwr/gnd plane loop inductance ? Chris -----Original Message----- From: Ray Anderson [mailto:Raymond.Anderson@xxxxxxx] Sent: Wednesday, October 23, 2002 11:51 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: pwr-gnd loop inductance measurment > >I'm trying to correlate pwr-gnd loop Inductance of a bga package >calculted from S11 and S21 measurement (VNA). > >FYI, For extracting the Inductance from S21 measurement , >1. I measure the capacitance of the vdd-gnd , >2. Short the BGA side (all vdd and gnd ball shorted together) >3. measurement the s21 on vdd-gnd on the top side (C4 pad). >4. Based on the first peak (resonance) I calculate the L . > >For S11, I think it is little more complicated, because we measure a >package with a very low impedance versus the 50Ohms cable, and maybe the >calibration is difficult ? Is someone have experience using S11 for the the >pwr-gnd loop inductance of a bga paclkage?.. Also is someone try to find >this very low loop inductance (a couple pH) with a TDR ?.. If yes, have you >seen any chalenges.? > >Thanks The S21 method you describe above is what we typically use in our lab for measuring package inductance as well as mounting pad/via inductances. We have achieved good correlation of our lab measurements with HFSS simulations of the same geometry. Your comments on the S11 measurements are correct. The calibration is difficult because it is very difficult to account for the probe inductance. Also, as you've pointed out, measuring small impedances with a 50 ohm instrument is error prone. S21 measurements have a much larger dynamic range. -Ray Anderson Sun Microsystems ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu